The invention relates to a pull cable system of a type having a cable for transmitting a pull force and a housing enclosing the cable for absorbing a pressure force, whereby the housing is comprised of a plurality of form-parts so joined to one another as to form a continuous axial throughbore and to enable an arcuate disposition of the housing.
The so-called Bowden pull wire that basically consists of a coiled steel wire casing and is traversed by a pull cable transmitting pull forces in a flexible manner without deflection rollers, compensating holders and supports is preferably used for operating the brakes or switching the gears of a bike.
The disadvantage of the Bowden pull wire is its coiled steel wire construction. When the wire is disposed in a curve, there are two differently stretched lengths to be compensated by forming slits at the outer radius by means of the resiliently coiled steel wire construction. When the pull cable is actuated, the compensating force can be supported only at the inner radius, which has the effect of pulling the Bowden pull wire into a stretched position. This can be prevented by the pull cable imposing this forced position. The result is a high friction resistance. The stronger the pull cable is being drawn, the larger is the friction resistance, the more ineffective is the force transmission, which presents a major disadvantage with regard to braking operations.
The variation in lengths occurring when bending the pull cable presents such a disadvantage that the Bowden pull wire is hardly suited for precise chain or hub gear shifting.
A narrow disposition of curves is not possible, which requires an unnecessary addition of length of the Bowden pull wire and thus causes higher costs, provides a disadvantageous optical appearance and long paths and thus hardly allows controlled dispositions.
It is an object of the present invention to provide an improved pull cable system in which the friction resistance is minimized and which exhibits a better directional stability, a much narrower and tension-free disposition in curves, a reduction of the contact surfaces of the pull cable by 75% and a removal of sliding restraints, as well as better armoring and sealing against outer influences.
According to the present invention, this object is solved by a pull cable system which includes a cable for transmitting a tensile force, a flexible tube for accommodating the cable, and a casing surrounding the tube for absorbing a pressure force, whereby the housing is composed of a plurality of congruent form-parts so joined to one another as to form a continuous axial passageway which is defined by an inside dimension, with the form-parts being so configured that abutting end faces between successive form-parts have a complementary configuration to thereby enable a disposition of the housing along an arcuate path, wherein the tube is defined by an outside dimension corresponding to the inside dimension of the throughbore.
Preferably, each of the form-parts has opposite end faces, with one of the end faces having a concave configuration and the other one of the end faces having a convex configuration. Thus, in accordance with the present invention, the coiled steel wire casing utilized in a conventional Bowden cable is replaced by joined complementary form-parts which permit transmission of great pressure forces by way of a ball pan configuration of adjoining end faces of successive form-parts.